This invention relates to the field of electrical power supplies, and more particularly to uninterruptible alternating current power supplies.
A typical uninterruptible power supply has an input connected to a source of a.c. power such as the power line system. This input is rectified and filtered, and used to charge or maintain charge on a storage battery which stores electrical energy for use during periods in which the power line system is undergoing a power outage. The rectified and filtered power, i.e. direct current power, is then inverted into a.c. power again which is then used to supply uninterruptible a.c. power to a variety of electrical equipment. Control of the inverter is provided by a separate circuit which is powered by rectified a.c. line power through a decoupling diode during normal operation or during periods of power line outage by rectified a.c. inverter output power through a decoupling diode. The disadvantage of this arrangement is that in case of a voltage drop in the interruption protected output lines, such as occurs during a short circuit, the power supply for the control circuitry and thereby the inverter can fail. Accordingly, it will be appreciated that it is highly desirable to supply the power to the inverter control circuit independently from the inverter output.
It is an object of this invention to provide an uninterruptible power supply which in the event of a power outage will securely maintain inverter control and operation even in the case of a voltage drop of the interruption protected output line. It is a further object of this invention to provide the power to the inverter control immediately upon an a.c. line power outage.